Astrocytes - Good Guys or Bad Guys?

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A prevailing dogma in spinal cord injury research was that astrocytes, one type of glial cells, prevents central nervous axon regeneration across a severe lesion by forming a scar.
Mark Anderson and Joshua Burda form the Michael Sofroniew lab challenged this long standing hypothesis in this work, that was also funded by Wings for Life. The results of their study, published in Nature, are surprising and suggest that the role of the scar forming astrcoytes is beneficial for regrowth and injury repair.

Focus on Astrcoytes
Dr. Sofroniew’s team investigated the role of astrocytes in the tissue repair after spinal cord injury. They used different models to prevent astrocyte scar formation or ablate the astrocytic scar in the chronic situation and then looked on the effects on axon regeneration after spinal cord injury. 
Surprisingly, the studies revealed that there was no axon regrowth when they prevented the scar formation by astrocytes, but instead caused pronounced larger lesions.
In a second approach, the scientists stimulated axon growth after spinal cord injury by infusing growth factors to the injury site with or without astrocytic scar forming conditions. In the presence of an astrocytic scar, robust regrowth was observed. When scar formation was prevented, regrowth was significantly reduced. Looking for molecular mechanisms, the team found that scar forming astrocytes as well as non-astrocyte cells express multiple axon–growth permissive molecules. This shows that scars are capable of producing chemical signals, albeit faint ones, that permit axons to grow over them.

“Scars may actually be beneficial”
“At first we were completely surprised when our early studies revealed that blocking scar formation after injury resulted in worse outcomes" says Michael Sofroniew, member of the Wings for Life Scientific Advisory Board. "And once we began looking specifically at regrowth, we became convinced that scars may actually be beneficial. Our results suggest that scars may be a bridge and not a barrier towards developing better treatments for paralyzing spinal cord injuries. This work opens the door to an area of research that has inhibited by an incorrect dogma.”